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Home » Security Advisories» NetBSD » Malformed ELF interpreter system crash

Malformed ELF interpreter system crash

A malformed copy of ld.elf_so, or any other elf interpreter, can cause a NULL pointer deference in the kernel.

  • Vendor: NetBSD
  • Vendor ID: 2006-008
  • Date: March 28, 2006


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NetBSD Security Advisory 2006-008
=================================

Topic: Malformed ELF interpreter causes system crash

Version: NetBSD-current: source prior to March 17, 2006
NetBSD 3.0: affected
NetBSD 2.1: affected
NetBSD 2.0.*: affected
NetBSD 2.0: affected

Severity: Any local user can crash the system

Fixed: NetBSD-current: March 17, 2006
NetBSD-3-0 branch: March 20, 2006
(3.0.1 will include the fix)
NetBSD-3 branch: March 20, 2006
NetBSD-2-1 branch: March 20, 2006
(2.1.1 will include the fix)
NetBSD-2-0 branch: March 20, 2006
(2.0.4 will include the fix)
NetBSD-2 branch: March 20, 2006

Abstract
========

A malformed copy of ld.elf_so, or any other elf interpreter, can cause
a NULL pointer deference in the kernel.

Technical Details
=================

The elf_load_file() function assumed that an interpreter always has a
PT_LOAD section defined in it's header. That is not necessarily the
case, as an attacker can trivially create an interpreter that
does not have that, and a binary that uses that interpreter.

The netbsd-2, netbsd-2-0 and netbsd-2-1 branches are only vulnerable
if the kernel is compiled with the USE_TOPDOWN_VM option which is
not set by default in GENERIC kernels.

Solutions and Workarounds
=========================

For all NetBSD versions, you need to obtain fixed kernel sources,
rebuild and install the new kernel, and reboot the system.

The fixed source may be obtained from the NetBSD CVS repository.

The following instructions briefly summarise how to upgrade your
kernel. In these instructions, replace:

ARCH with your architecture (from uname -m), and
KERNCONF with the name of your kernel configuration file.

To update from CVS, re-build, and re-install the kernel:

# cd src
# cvs update -d -P sys/kern/exec_elf32.c
# ./build.sh kernel=KERNCONF
# mv /netbsd /netbsd.old
# cp sys/arch/ARCH/compile/obj/KERNCONF/netbsd /netbsd
# shutdown -r now

For more information on how to do this, see:

http://www.NetBSD.org/guide/en/chap-kernel.html


Thanks To
=========

Eric Haszlakiewicz for PoC code and implementing the fixes.
Coverity for access to the scans of the NetBSD source code.

Revision History
================

2006-03-29 Initial release


More Information
================

Advisories may be updated as new information becomes available.
The most recent version of this advisory (PGP signed) can be found at
ftp://ftp.NetBSD.org/pub/NetBSD/security/advisories/NetBSD-SA2006-008.txt.asc

Information about NetBSD and NetBSD security can be found at
http://www.NetBSD.org/ and http://www.NetBSD.org/Security/.


Copyright 2006, The NetBSD Foundation, Inc. All Rights Reserved.
Redistribution permitted only in full, unmodified form.

$NetBSD: NetBSD-SA2006-008.txt,v 1.5 2006/03/29 11:14:28 adrianp Exp $

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